Method of reducing barrel wear



April 28, 1964 B. BERGHAUS 3,130,671

METHOD OF REDUCING BARREL WEAR Filed May 2, 1958 tau.

INVENTOR 5EKA4/4/PD 55PAws TORNEY enriched with foreign matter for otherreasons.

3,13%,671 METHQD OF REDUCING BARREL WEAR Bernhard Berghaus, Zurich,Switzerland, assignor to Elektrophysikalische Anstait Bernhard Berghaus,Vaduz, Liechtenstein, :1 corporatian of Liechtenstein Filed May 2, B58,Ser. No. 732,605 5 Claims. (Cl. 102-93) The present invention relates toa method of reducing the Wear of the inner barrel wall of firearmsduring the passage of projectiles, in particular in firearm barrels ofwhich the inner wall has a surface layer enriched with a foreignsubstance. The present invention is based on the generally known factthat firearm barrels are subject to a reduction in weight during firing,which is caused by the small quantity of liquid or vaporous barrelmaterial ejected as each projectile is fired. Apparently the temperatureat the points of the inner barrel wall subject to the greatest stressrises above the melting point during firing, at least in a thin surfacelayer, so that the inner wall melts at thesepoints.

It seems natural for the resistance to wear of such firearm barrels tobe increased by raising the melting point of the firearm barrels or atleast of their inner wall. However, this is not possible as alloyedsteels must be used for the barrel for reasons of strength while thesurface zone of the inner wall is generally improved by enriching itwith foreign substances, i.e. hardened by nitriding. Owing to the-alloycomponents and the surface layer enriched with foreign substances, themelting point of the material of the inner wall is usually reduced. Thepresent invention has for its object to eliminate the drawbacks of thislowering of the melting point of the inner barrel wall in firearms ofwhich a surface layer is The method according to this invention ofreducing the wear of the inner barrel wall of such firearms during thepassage of a projectile is characterized by the fact that at least thedriving bands of the projectile and at least their surface have themelting point of their material reduced at least substantially to themelting point of the inner barrel wallor provided with a lower meltingpoint than the latter.

I Theinyention also relates to a.firearm and a projectile designedaccording to this method and characterized by.

the fact that at least the surface portions designed for contact and theadjacent deeper zones are enriched with materials of such kind that theprojectile driving .bands possess approximately the same or a lowermelting point than the inner barrel wallunder the prevailing pressureconditions.

The method is described in greater detail in conjunction withtheattached drawing which illustrates an embodiment of the treatment ofprojectiles according to the present invention.

In present-day firearms the inner wall of the barrels is subject to veryhigh stresses and it reaches a temperature, particularly in automaticquick-firing guns, which is near the melting point of the raw material.This has the result that a measurable quantity of fused or vaporizedmaterial leaves the barrel with' the projectile during firing. Insofaras such material comes from the driving band of the projectiles, nodrawbacks need be anticipated. But if the material ejected stems fromthe inner barrel wall, this definitely involves a highly undesirablewear of the barrel, at any rate where the material has beenremoved.Weighing of the barrels of quick-firing guns prior and subsequent tofiring revealed Weight losses of up to 100 gms.

- In order to improve the life of the heavy-duty barrels of tfirearms,such'barrels have their inner wall improved,

United States Patent 0 preferably by nitriding according to Swiss PatentNo. 308,295.

It has been found that tests performed with projectiles previouslysubjected to various treatments resulted in a reduction of the quantityof material removed from the inner barrel wall by melting. Such areduction of wear was always noticed when the melting point of thematerial of the driving band Was at least substantially. reduced so asto approach the melting point of the inner barrel wall or loweredbeneath that value. Apparently a certain quantity of fused and vaporizedmaterial is necessary for the passage of the projectiles through suchfirearm barrels; if the melting point of at least the projectile drivingbands is lower than the melting point of the inner barrel wall, thefused material is largely supplied by these projectile portions and notby the inner barrel wall. This protection of the inner barrel wall wouldappear to have caused the noticed improvement of the resistance to wearand of the' life.

Naturally it is not necessary that the melting point of the projectiledriving bands be reduced exactly to the melting point of the surfaceportions of the inner barrel wall since an approximate adjustmentsuflices to result in a marked improvement of the life. By way ofexample, compared with projectiles without nitrided steel driving bands,a substantial prolongation of the life of gun barrels of which the innerwalls had been nitrided according to the method disclosed in SwissPatent No. 308,295 was obtained when steel projectiles having nitridedsteeldriving bands were used. i i

It is particularly advantageous to adjust the melting point of theprojectile driving bands to the melting point of the inner barrel wallby forming at least the said bands of a steel of which the melting pointhas been lowered by diifusing suitable foreign substances into it. Byway of example, if the steel driving bands of steel projectiles are tobe annealed and simultaneously enriched with nitrogen, an arrangementaccording to FIG. 1 can be employed. To this end, an evacuabledouble-walled and coolable gasdischarge vessel 1 with a removable lid 2has its interior provided with a metallic supporting plate 3 oninsulators '4 carrying resilient metal pins 5 designed to have the steelprojectiles 6 slipped 'over them. Arranged parallel with the supportingplate 3'and conductively connected therewith is a metallic orifice plate7 arranged in a plane with the driving bands 8 of the projectiles 6 andprovided with circular holes 9 through which the projectiles 6 project.The thickness of the orifice plate 7 is such as to cause the inner sideof the holes 9 to register with the two driving bands 8. This inner sideofthe holes 9 mustenclose the driving bands 8 concentrically and form anannular gap with them which is of the same width throughout.

v The supporting plate 3 and the orifice plate 7 are connected with thenegative pole of the pair of terminals 11 via an insulated voltagelead-in 10, while the positive connection is effected with the metallicdischarge vessel 1. In the discharge vessel 1, 2, suitable means (notshown) are provided to produce a gas atmosphere comprising 30% N and Hat a pressure of 5 to 10 mm. Hg, and to maintain it during operation.After completion of a starting cycle, a glow discharge is produced at avoltage of 400 to 500. volts between the discharge vessel 1 and theprojectiles 6 and on the orifice plate 7 connected to the same voltage.This glow discharge produces a particularly elevated energyconcentration of .1 to 10 watts/cm. of the surface of the. driving bands8 between the said bands and the inner Wall of the holes 9 if the widthof the annular gap is suitable. This operative condition, which istermed hollow-cathode effect, is described in detail in the Swiss PatentNo. 314,340. The driving bands 8 reach the desired glow temperatureduring this type of operation within a short space of time, e.g. .5 to 2minutes, and are enriched with nitrogen owing to the ion bombardment.The high energy density in the annular gapensures a comparatively rapiddiffusion of the atomic nitrogen into the driving bands so that thenecessary penetration depth is obtained after annealing, and thetreatment can be discontinued. Within the relatively short period oftreatment the projectile 6 has the temperature of its other portionsincreased so slightly only that its strength is not affected.

When the treatment gases are diffused into the metal surface, i.e. thenitrogen in the example disclosed above, so called solid solutions areformed which constitute chemical and physical combinations of metal andgas. Experience has shown that such solid solutions-also under theextreme pressure conditions during firing-result in a reduction of themelting point of the steel driving bands to a value which correspondsapproximately to the melting point of the inner wall of gun barrelsnitrided according to the above-mentioned Swiss Patent No. 314,340.

Apart from the above-mentioned nitrogen and according to theapplication, many other substances are suitable. By Way of example, theprojectile portions can be enriched with phosphorus or with sulphur,either in elementary form, dissolved in the metal involved, as solidsolution, or in the form of suitable compounds.

Finally, other gases, such as hydrogen, oxygen and under certainconditions-even rare gases may be concentrated in the projectileportions in question in such a form that they can contribute to reducingthe melting point.

As in the example described above, the substances to be concentrated inthe projectile driving bands may be obtained mainly from the gas in thedischarge vessel. Naturally such foreign substances may also be appliedin some other manner to the projectile surfaces to be treated in theglow discharge.

By way of example, a suitable substance may be vaporized in thedischarge vessel and mixed with the gas atmosphere, or a correspondingmist formed of such material particles is sprayed into the dischargevessel. In addition, the known process of cathode atomization or arcdusting may be employed to mix the foreign particles with the gasatmosphere.

The present method is of course not limited to the treatment ofprojectiles which have at least the driving bands adjusted to the gunbarrel by means of an electric gas or glow discharge and by enrichmentwith foreign substances. Enrichment with foreign substances may also beobtained in some other manner, by way of example by diffusion inheatable furnaces or by treatment in melts containing the said foreignsubstances. sible to form the projectiles or at least their drivingbands of materials of which the melting point is already adjusted tothat of the associated gun barrel without additional treatment.

The improvement of the life of gun barrels performed in the mannerdisclosed and the present method of treating projectile driving bands isprobably also the result of the simultaneous formation of a gaseousslide film on the surfaces in engagement. It has been known for sometime that a gas layer between the metal surfaces of firearm barrels andprojectiles sliding on one another at a high pressure per unit area cansubstantially reduce friction. The gaseous lubricant film is notsupplied to the contacting surfaces from outside but provided byvaporization of gas-generating materials from the surfaces in engagementor the issuance of gas components dissolved in the metal or combinedwith the metal surface, which is naturally possible only under highsurface pressure. Naturally normal unprepared sliding surfaces cannotmaintain a gaseous lubricant film for any length of time since a certaingas loss by diffusion into the as- It is also pos- 4 sociated surfaceand by the passage towards the edges of the sliding surface portions isinevitable.

It has therefore been proposed to increase the gas supply by thesurfaces subject to sliding friction of the barrel and projectilerespectively by charging their surfaces with gases or by diffusing gasgenerating substances into them. Phosphorus, sulphur, certain metals,oxygen etc. are suitable materials. It has also been proposed to designthe driving bands of the projectiles correspondingly and to enrich themwith gas generating substances, i.e. to charge them with gas at thesurface, instead of treating the inner wall of the gun barrels, whichare difficult to process. Attempts at obtaining a further reduction ofsliding friction by influencing the degree of enrichment in the metalsurfaces involved (distribution of depth, concentration etc.) have beenunsuccessful and revealed only a slight influence on the maximumreduction of friction.

It was astonishing to find a further improvement of the life of firearmbarrels after lowering the melting point according to the presentmethod, if a material component is provided at least in the projectiledriving bands which release that foreign substance under the conditionsobtaining during firing which has been concentrated in the inner surfaceof the barrel.

in the gun barrels having their inner wall enriched with nitrogen by anelectric glow discharge, the surface portions engaged by the projectilecan easily supply the quantity of gas required for the formation of gaspads. During the passage of standard projectiles provided withunprepared driving bands it would seem that a. certain quantity of gasis used and thus results in a detrimental reduction of the gaseouslubricant film.

Conditions are somewhat different with the application of gas nitridedprojectile driving bands, which has already been experimentallyattempted at an earlier date, in standard, i.e. not specially prepared,gun barrels. The driving bands nitrided in conventional baths orfurnaces could, however, supply a friction-reducing gas pad while thebarrels were still cold, but during rapid fire this advantageous gaslayer could not be maintained. Apparently the heated inner barrel wallabsorbs the gases emerging from the driving bands far too rapidly for a.gaseous lubricant film to be maintained.

With the present method, both the gun barrels and the driving bands ofthe projectiles which will contact their inner walls are enriched withsuitable substances, e.g. in an electric glow discharge. I

The tests made in this connection revealed a further improvement of thelife of firearm barrels beyond the values previously obtained if :amaterial component was provided in the projectile driving bands whichwill release that foreign substance in firing with which the inner Wallof the barrel has been enriched. The gas layer formed when the highsliding friction occurs is no longer supplied by the inner barrel wallas. hitherto and more or less absorbed by the driving bands. The drivingbands contribute to the supply of the gas layer. If the driving bandsbecome heated during their passage through the barrel when single roundsare fired, the reduction of gas generating substances in the innerbarrel wall is largely prevented since just those substances [aresupplied by the driving bands and partly diffused into the heated innerbarrel Wall with which the latter has been enriched and improved.

Both surfaces are preferably enriched with the same gas generatingsubstance. However, different substances may be employed provided thatthe projectile driving bands supply those gaseous components with whichthe inner barrel wall has already been enriched.

Furthermore, it is important that the concentration of the gasgenerating substances enriched in the two metal surfaces are adapted toone another. As gun barrels must advantageously be nitrided in anelectric gas or glow discharge in order to obtain a hardened but ductileand shatterproof inner surface, it is recommended to enrich the entireoutside of the projectile, or at least the projectile portions designedto contact the said inner wall, in an ionized gas atmosphere with thesame gas generating substances although the present method is notlimited to this treatment of the projectiles.

'lhe gas generating substances can either enrich, as chemical compounds,the topmost zonesof the projectile driving bands, or form alloycomponents of the metals employed or a solid solution with the metal.Apart from such chemical compounds, metals and metalloids are suitableas alloy components when concentrated in the inner barrel wall, by wayof example zinc, lead, etc. In all cases, the desired reduction of themelting point is obtained as well.

In the treatment disclosed in conjunction 'with the drawing, of metalsurfaces in a glow discharge, the surface structure by materialmigration caused by dissolving minute metal particles from the surfacezone is altered also when the said surfaces are n'ot heated to annealingtemperature as in the above example. It is not exactly known whether themetal particles are dissolved out of the crystal structure owing tovaporization at the points of impingement of individual ions or owing todirect shock release. At any rate, experiments reveal migration of thematerial. At the same time material is also added since the gasatmosphere is intermingled with metal particles stemming from thesurface of the 'work itself or from the counter-electrode, and suchmetal particles are electrically charged in the glow chamber,accelerated in the direction of the work surface and impinge on thelatter with a high kinetic energy.

The extent of the material migration in one or the other direction canhe influenced by suitable selection of the geometric arrangement of thework and the counterelectrode as well as by the pressure in thedischarge vessel and the type and polarity of the voltage. Theconditions of the discharge are advantageously so selected that materialremoval is preponderant. At any rate, the surface of the work isprovided, after maintaining the glow discharge for a sufficient space oftime, which is only a few minutes in the example described, but may behours, with a surface zone on the metal body which displays a highlyuniform micro-porosity, which is likely to extend into moleculardimensions. At the same time, this surface zone has a strength notmarkedly inferior to that of unaltered metal layers.

This micro-porous surface layer keenly enriches itself with the gaspresent in the discharge vessel and retains this gas charge also aftercompletion of the treatment and under atmospheric conditions.

After this glow-discharge treatment, the surface is enniched with gas intwo respects. On the one hand, nitrogen diffused into it is dissolved inthe metal layer or combined in the form of a solid solution. On theother hand, gaseous components are enclosed or adsorbed in themicro-porous surface layer. Under the pressure and temperatureconditions prevailing in firing, both the gas charge and the solidsolutions contribute to the supply of the friction-reducing gas layerbetween the metal surfaces sliding on one another. As regards thedriving bands, the gas charge is likely to be effective at the outsetwhile substantially deeper zones having solid solutions contribute tothe supply of gas after deformation has begun.

Depending on the foreign substances concentrated in the inner barrelwall and apart from the above-mentioned solid nitrogen-metal solutions,many other substances are suitable to supply gas. By way of example, theprojectile portions can be enriched with sulphur either in elementaryform, dissolved in the metal involved as a solid solution, or in theform of suitable compounds. Such substances evaporate under the extremepressures and temperatures prevailing and form the friction-reducing gaslayer. Finally, other gases, such as hydrogen, oxygen andunder certainconditionsrare gases may be concentrated in the metal surfaces subjectto friction so that they may contribute to the formation offrictionreducing gas layers in order to avoid a reduction of the saidsubstances in the inner barrel wall.

It may also be pointed out that the friction-reducing gas pad isadvantageous for firearms owing to the chicient sealing of theprojectile in the barrel. The pressurereducing gas layer obtained alsoseems to form a protective layer for the portions of the inner barrelwall subject to particular stress against the aggressive explosionproducts. It may be possible that the marked improvement of the life offirearm barrels obtainable by means of this method is not caused by thereduction of the losses due to sliding friction itself, but to thereduction of detrimental effects of the usually high sliding friction,such as wear, increased danger of erosion etc.

I claim:

1. Method of reducing wear of the inner wall of a steel gun barrel,hardened by nitriding, by the passage therethrough of projectiles onfiring, the driving bands of the projectile being made of a ferrousmaterial having a higher melting point than the hardened barrel innerwall, comprising heating the projectile driving bands in a mediumcontaining a substance which diffuses into the surface zones of theprojectile driving bands which later, on firing, slide along the barrelinner wall and are capable of developing and releasing gases or vaporsat the temperature occurring on firing which build up a frictionreducingfilm between the barrel wall and the driving bands, and continuing thetreatment to cause said substance to diffuse into the driving bands insuch amount that the melting point of the surface zones of the drivingbands, enriched with such substance, is reduced down to or below themelting point of the hardened surface zone of the barrel inner wall.

-2. Process according to claim 1, wherein the medium in which thedriving bands are heated is a gaseous or vaporous atmosphere containingthe said substance.

3. Process according to claim 2, in which the driving bands are heatedby an electric glow discharge in the said atmosphere.

4. Process according to claim 1, wherein the medium in which the drivingbands are heated comprises an atmosphere containing nitrogen.

5. Process according to claim 1, wherein the driving bands to be treatedpossess a microporous surface zone.

References Cited in the file of this patent UNITED STATES PATENTS1,837,256 Egan Dec. 22, 1931 1,861,522 Brandt June 7, 1932 2,411,073Whitney Nov. 12, 1946 2,437,249 Floe Mar. 7, 1948 2,701,524 Van DineFeb. 8, 1955 FOREIGN PATENTS 589,069 Great Britain June 10, 1947 744,753Great Britain Feb. 15, 1956

1. METHOD OF REDUCING WEAR OF THE INNER WALL OF A STEEL GUN BARREL,HARDENED BY NITRIDING, BY THE PASSAGE THERETHROUGH OF PROJECTILES ONFIRING, THE DRIVING BANDS OF THE PROJECTILE BEING MADE OF A FERROUSMATERIAL HAVING A HIGHER MELTING POINT THAN THE HARDENED BARREL INNERWALL, COMPRISING HEATING THE PROJECTILE DRIVING BANDS IN A MEDIUMCONTAINING A SUBSTANCE WHICH DIFFUSES INTO THE SURFACE ZONES OF THEPROJECTILE DRIVING BANDS WHICH LATER, ON FIRING, SLIDE ALONG THE BARRELINNER WALL AND ARE CAPABLE OF DEVELOPING AND RELEASING GASES OR VAPORSAT THE TEMPERATURE OCCURRING ON FIRING WHICH BUILD UP A FRICTIONREDUCINGFILM BETWEEN THE BARREL WALL AND THE DRIVING BANDS, AND CONTINUING THETREATMENT TO CAUSE SAID SUBSTANCE TO DIFFUSE INTO THE DRIVING BANDS INSUCH AMOUNT THAT THE MELTING POINT OF THE SURFACE ZONES OF THE DRIVINGBANDS, ENRICHED WITH SUCH SUBSTANCE, IS REDUCED DOWN TO OR BELOW THEMELTING POINT OF THE HARDENED SURFACE ZONE OF THE BARREL INNER WALL.